Ever heard of a ej18/ej22t hybrid? My thinking is along the the same lines as the honda mighty mini build of the d16y8 block with d16b1 non-vtec heads, low compression for turbo application.

I don't know the ins and outs of the boxer motor, but if the 2.2t heads and 2.2t internals go into the 1.8 block it would have low enough compression to sustain good boost pressures.

The EJ18E shares it's internals w/EJ20E, EJ20D, & EJ22E, & they have the same strength as those found in the 22T, so there is no need to swap internals. There are people out there boosting them the way that they are because they are apparently very strong little engines.

The heads of the 18E are very similar to those of the 22T/E to the point where you cannot tell the difference between them externally. Internally, the 18E heads would be suitable for boost if they were drilled & tapped & had 22T cams in them. Other than that, there is no need to change heads, IF your head gasket is thick enough.
I believe that the 18E heads have a lower cc than that of the 22E/T heads. I'll have to double check on that.

The REAL question is whether or not one can put DOHC heads on an 18E block, like 25D heads or 20K heads, for example. That would be a great upgrade for 18E blocks.